In economically developed countries, cardiovascular disease still represents a major cause of mortality. In particular, abnormal coagulation and inappropriate thrombus formation within blood vessels precipitates many acute cardiovascular disease states. While it has long been recognized that a variety of plasma proteins such as fibrinogen, serine proteases, and cellular receptors are involved in hemostasis, it is the abnormal regulation that has emerged as important contributing factors to cardiovascular disease. Thrombin can be considered the key or principal regulatory enzyme in the coagulation cascade; it serves a pluralistic role as both a positive and negative feedback regulator in normal hemostasis. However, in some pathologic conditions, the former is amplified through catalytic activation of cofactors required for thrombin generation such as factor Xa. Factor Xa, as part of the prothrombinase complex composed of non-enzymatic cofactor Va, calcium ions, and a phospholipid membrane surface regulates the generation of thrombin from its zymogen prothrombin. Furthermore, the location of the prothrombinase complex at the convergence of both the intrinsic and extrinsic coagulation pathways suggests that inhibition of factor Xa, and hence thrombin generation, may be a viable approach to limiting the procoagulant activity of thrombin.
Indeed, ample evidence exists for the role of factor Xa inhibitors as anticoagulants. Antistasin, a potent inhibitor of blood coagulation factor Xa from the Mexican leech: Haementeria officinalis, displays antithrombotic activity in various models of arterial and venous thrombosis (Lapatto et al., Embo. J., 1997:5151-5161). Other protein or polypeptide factor Xa inhibitors include recombinant tick anticoagulant peptide (rTAP), which is known to accelerate the recombinant tissue plasminogen activator mediated clot lysis and prevent acute reocclusion in the dog, hence indicating factor Xa inhibitors may be useful as an adjunct to thrombolytic therapy (Mellott et al., Fibrinolysis, 1993:195-202). Furthermore, in a canine coronary artery electrolytic lesion model, rTAP was demonstrated to reduce thrombus mass and time to occlusion in the absence of dramatic hemodynamic or hemostatic changes indicating the primary role for factor Xa in the process of arterial thrombosis (Lynch et al., Thromb. Haemostasis, 1995:640-645; Schaffer et al., Circulation, 1991:1741-1748). On the venous side, rTAP was also demonstrated to reduce fibrin deposition in a rabbit model of venous thrombosis while having little affect on systemic hemostatic parameters (Fioravanti et al., Thromb. Res., 1993:317-324). In addition to these relatively high molecular weight proteins that are not suitable as oral antithrombotic agents, there also exist examples of low molecular weight factor Xa inhibitors. In particular, DX9065a, a low molecular weight synthetic factor Xa inhibitor, has also shown antithrombotic potential in various experimental thrombosis rat models. In both arteriovenous shunt and venous stasis models, inhibition of thrombus formation was achieved at doses that had little effect on APTT, indicating that DX9065a is effective in preventing thrombosis and hence has therapeutic antithrombotic potential (Wong et al., Thromb. Res., 1996:117-126).
The majority of factor Xa inhibitors known to date have been previously summarized in two reviews (Edmunds et al., Annual Reports in Medicinal Chemistry, 1996:51 and Kunitada and Nagahara, Curr. Pharm. Des., 1996:531-542). However, it is readily apparent that there still exists a need for more effective agents that regulate factor Xa proteolytic activity.
Some quinoxalinones have been reported, and these compounds have displayed marked pharmacological activity: Japanese Application: JP 88-99097 880421; Japanese Application: JP 89-254348 890929; CAN 116: 83686; World Publication 9707116; Otomasu et al., Yakugaku Zasshi, 1970;90(11):1391-1395; Seth M et al., Indian J. Chem., 1974;12(2):124-1288; Japanese Patent 63145272; Sparatore et al., Farmaco, 1989;44(10):945-950; and F. Hahn et al., Arch. Int. Pharmacodyn. Ther., 1992:108.
None of the above articles set forth above disclose or suggest compounds of Formula I that are inhibitors of serine proteases involved in the blood coagulation cascade.